PSY 100 – General Psychology
Lecture Guide 7: Sensation and Perception
Michael L. Thomas, PhD
1 Introduction and Learning Objectives
🎥 Watch this before starting!
2 Sensation and Perception
Sensory input refers to how physical forms of energy—such as light, heat, sound, and pressure—are translated into (bio-) electrical signals that the brain can understand. This conversion process is called transduction. Each sense organ is equipped with specialized sensory receptors designed to detect and convert a specific type of physical stimulus. For example, visual receptors in the eye contain chemicals that react to light waves, initiating the process of transduction for vision.
Once activated, sensory receptors transmit information via neural impulses to specific areas of the brain that are dedicated to processing that type of sensory input. For instance, visual signals are sent to the primary visual cortex, auditory signals to the primary auditory cortex, and touch-related signals to the primary somatosensory cortex.
These receptors do more than simply detect the presence of a stimulus—they also code for the intensity and quality of the energy. A more intense stimulus—like a firm touch—tends to produce faster firing rates in neurons. However, over time, if a stimulus remains constant, neurons may reduce their firing rate. This is known as sensory adaptation, and it helps prevent sensory overload.
This organization of sensory pathways allows us to experience the world in a coherent and meaningful way. Although all sensory input begins as raw physical energy, that energy becomes the basis of our perception—the stream of conscious experience that defines how we see, hear, feel, and interact with our environment. Perception is how the brain organizes and interprets that sensory information.
👁 Think of sensation as data input and perception as data interpretation.
There are five traditionally recognized major senses:
1. Vision (visual perception)
2. Hearing (audition)
3. Touch (somatosensation)
4. Taste (gustation)
5. Smell (olfaction)
However, this list can be extended to include additional senses such as:
- Pain (nociception)
- Balance (vestibular sense)
- Body position and movement (proprioception)
- Temperature (thermoception)
Of all these, vision has been studied most extensively in psychological and neuroscientific research.
3 Sensitivity
How sensitive are the major senses? This sensitivity is often studied using psychophysical methods (i.e., psychophysics), which examine the relationship between stimulus intensity and detection. Researchers measure sensitivity using a function that plots the probability of detection as a function of stimulus intensity. This relationship often takes on an S-shaped curve, known as a psychometric function. The point at which a stimulus is detected at least 50% of the time is called the absolute threshold. This threshold represents the minimum intensity at which a stimulus becomes reliably perceptible. Examples of real-world absolute thresholds for the major senses are shown in the table below.
| Sense | Absolute Threshold |
|---|---|
| Vision | A candle flame seen from 30 miles away on a clear, dark night |
| Hearing | The tick of a watch at 20 feet |
| Taste | One teaspoon of sugar in two gallons of water |
| Smell | One drop of perfume throughout a three-room apartment |
| Touch | A bee’s wing falling on your cheek from a height of about half an inch |
These classic examples assume near-perfect conditions (e.g., dark-adapted vision, minimal background noise/odors, practiced observers, and a neutral decision criterion). In everyday settings, thresholds are typically higher (worse) due to lighting, noise, attention, individual differences, and response bias (signal-detection considerations). Treat the numbers as heuristic demonstrations, not precise limits.
The minimal change in a stimulus that can just barely be detected is called the just noticeable difference (JND). This difference is proportional to the initial intensity of the stimulus. Some examples of JNDs are shown in the table below.
| Stimulus Type | JND Estimate |
|---|---|
| Light Intensity | 8% |
| Sound Intensity | 5% |
| Odor Concentration | 15% |
| Electric Shock | 1% |
| Lifted Weights | 2% |
Note that JNDs are expressed as percentages. This means the JND is a constant ratio, not a fixed amount—an idea known as Weber’s Law (or Weber–Fechner law). For example, Weber’s Law predicts that you would likely notice the difference between a 10 lb weight and a 10.2 lb weight (a 2% difference), but not between a 100 lb weight and a 100.2 lb weight (a 0.2% difference) even though in both cases the difference is 0.2 lbs. However, you would likely notice the difference between a 100 lb weight and a 102 lb weight (a 2% difference), because the proportion remains consistent.
🔎 Explore This (Optional):
Psychophysics concepts such as the JND are used every day in multiple industries. Follow this link to a Radiant Vision Systems webpage that discusses applications of the JND in examining visual display quality.
4 Vision
4.1 Transmission and Transduction
We generally refer to the physical energy detected by our eyes as light, a form of electromagnetic energy that radiates from the sun and other sources. Humans can perceive electromagnetic wavelengths in the 400 to 700 nanometer range (approximately fifty percent of sunlight reaching the Earth’s surface is visible light), known as the visible spectrum. This range is not arbitrary—most other wavelengths are blocked by the Earth’s atmosphere, which likely explains why our visual system evolved to be sensitive to this specific band of energy.
Vision begins at the eye, which contains several structures that work together to capture and focus light:
- Cornea: The cornea is a transparent, protective outer layer covering the front of the eye. Light first passes through this surface.
- Lens: The lens is a flexible structure that changes shape to help focus light on the retina. It becomes more spherical for near objects and flatter for distant ones.
- If the lens doesn’t flatten sufficiently, distant objects appear blurry—a condition known as nearsightedness (myopia).
- If the lens doesn’t become spherical enough to focus on nearby objects, the result is farsightedness (hyperopia).
- If the lens doesn’t flatten sufficiently, distant objects appear blurry—a condition known as nearsightedness (myopia).
- Pupil: The pupil is a circular opening that regulates how much light enters the eye. It dilates (enlarges) in low light and constricts (shrinks) in bright light.
- Iris: The iris is the colored part of the eye. It contains muscles that control the size of the pupil in response to lighting conditions. The iris gets its color from melanin, and different amounts of melanin determine eye color.
These components work together to transmit light through the eye and focus it onto the retina, a layer of neural tissue at the back of the eye. This is where transduction occurs—the process by which photoreceptors convert physical light energy into electrical signals that the brain can interpret. The retina contains two main types of photoreceptors: rods, which are sensitive to low light and support black-and-white vision, and cones, which detect color and fine detail in brighter light.
Rods are highly sensitive to light and are essential for night vision, but they do not detect color—they support achromatic (black-and-white) vision. Cones, in contrast, are responsible for daylight and color vision. They require more light to function and enable us to perceive fine detail and vibrant color.
These receptors are not evenly distributed across the retina. Cones are densely packed in the fovea, the center of the retina, which is the region of highest visual acuity. Rods are concentrated in the periphery of the retina, making them especially useful for detecting motion and dim light in the outer edges of our visual field.
🌌 Fun fact! At night, you may see objects more clearly by looking slightly to the side, allowing light to fall on the rod-rich periphery rather than the cone-rich fovea. This is called averted vision.
Photopigments, which are light-sensitive chemicals found in rods and cones, absorb incoming light. This absorption initiates a cascade of events that leads to the generation of a neural impulse. These impulses are transmitted to the brain via the optic nerve.
The optic nerve is made up of the axons of ganglion cells, which carry visual information from the retina to the occipital lobe of the brain, where visual processing occurs. The entire route that visual signals take from the retina to the brain is called the optic tract, and the optic nerve is the first segment of this pathway.
👁️ Fun Fact: You have a blind spot in each eye where the optic nerve exits the retina—there are no rods or cones in this area! But don’t worry—your brain cleverly fills in the gap, so you almost never notice it’s there.
Take a close look at the image below. Do you notice anything unusual? You might observe that faint gray dots appear at the intersections of the white lines—but when you focus directly on one of those intersections, the gray dot disappears.
This visual phenomenon is known as the Hermann Grid Illusion. One theory suggests that it happens because your retinal ganglion cells inhibit surrounding retinal ganglion cells when they detect light. Thus, since a point at an intersection is surrounded by more areas of light intensity than a point in the middle of a line, the intersection appears darker due to increased lateral inhibition.
4.2 Visual Acuity
Visual acuity refers to the eye’s ability to detect and resolve fine details. It is most commonly measured using the Snellen chart, which assesses how well a person can read letters or symbols at a specific distance.
The standard measure of visual acuity is 20/20 vision. This means that the person can read at 20 feet what a typical viewer with normal vision can also read at 20 feet. If someone has 20/100 vision, it means that they must be 20 feet away to see what a person with normal vision could see from 100 feet away. This indicates reduced visual clarity and may require corrective lenses.
4.3 Color Vision
The perception of color is typically described using three main qualities: hue, brightness, and saturation. Hue refers to the property we most closely associate with the name of a color (such as red, green, or blue) and is determined by the wavelength of electromagnetic energy, measured in nanometers (nm). Brightness refers to the intensity of the color, which is influenced by the number of photons reflected from a colored surface. Saturation describes the purity of a color, or how much gray is mixed into it—highly saturated colors appear vivid, while low-saturation colors look more washed out or pale.
Humans can distinguish around 150 unique hues, corresponding to different wavelengths within the 400 to 700 nm range of the visible spectrum. All of these hues can be reproduced by mixing different combinations of just three primary colors of light: red, green, and blue. For instance, combining red light (~650 nm) and green light (~500 nm) produces a mixture that closely resembles yellow light (~575 nm). This process of mixing applies specifically to light, not pigments or paints, which follow different physical rules.
People with typical color vision are known as trichromats, meaning they have three types of cone cells sensitive to different wavelengths. Some individuals, known as dichromats, have only two functioning types of cones and therefore have limited color perception. Monochromats lack functioning cone cells entirely and see only in shades of gray.
Color vision deficiency, often called color blindness, comes in several types. The most common form is red-green color deficiency, where people have trouble distinguishing between reds and greens, due to reduced sensitivity or absence of red or green cone cells. Less common is blue-yellow color deficiency, where distinguishing between blues and greens or yellows and reds becomes difficult, caused by reduced sensitivity or absence of blue cone cells. A very rare type is complete color blindness, or achromatopsia, where people see only shades of gray and often have other vision problems like light sensitivity and reduced visual sharpness. Color blindness is far more common in males, affecting about 8%, compared to just 0.5% of females, due to genetic differences.
🔎 Explore This (Optional):
Want to learn more about how color blindness affects daily life and education? Visit the Colour Blind Awareness website for insights, resources, and practical advice on living with color vision deficiency.
The Young-Helmholtz Trichromatic Theory proposes that human color vision is based on the activity of three types of color receptors (cones) located in the retina. Each type of cone is sensitive to a different range of wavelengths: one responds primarily to red light, another to green, and the third to blue. According to this theory, our ability to perceive a full range of colors arises from the combined activation of these three types of cones. By blending signals from red, green, and blue receptors, the brain is able to construct the perception of millions of different colors. This theory also provides an explanation for color blindness (i.e., as being caused by a deficient cone type).
However, the trichromatic theory does not account for all aspects of color perception. One notable limitation involves the phenomenon of afterimages. For instance, when participants stare at a brightly colored light for an extended period and then shift their gaze to a neutral background, they often see a complementary color—an effect the trichromatic theory alone cannot fully explain. To experience an afterimage, stare at the center of this image for about 30 seconds, and then afterward quickly at the blank white space below the image:
What do you see? For people with typical color vision, if the illusion worked correctly, you should have seen a brief afterimage of a face in more natural colors. The Young-Helmholtz Trichromatic Theory cannot explain this effect.
This limitation led to the development of a complementary theory: the Opponent-Process Theory, which helps account for afterimages and certain patterns of color perception. The Opponent-Color Theory, proposed by Ewald Hering, suggests that color perception is controlled by opposing pairs of color-sensitive neurons. According to this theory, there are two primary color-opponent systems in the visual system: a red-green unit and a blue-yellow unit. Each unit consists of neurons that are excited by one color in the pair and inhibited by the other.
This theory helps explain certain visual phenomena that the trichromatic theory cannot—particularly the experience of afterimages. For example, if you stare at a red image for a prolonged period and then look at a white surface, you may see a green afterimage. This occurs because the red-green unit becomes fatigued from prolonged stimulation, and when the stimulus is removed, the opponent (green) response is temporarily stronger, resulting in a visible afterimage.
Today, researchers believe that both the Young-Helmholtz Trichromatic Theory and the Opponent-Process Theory are correct and work together to explain how we perceive color. Trichromatic processing occurs at the level of the cones in the retina, while opponent-process coding occurs further along the visual pathway, particularly in the retinal ganglion cells and beyond.
4.4 Eye Movements
Although it may feel like your eyes move smoothly when you scan a scene, they actually make rapid, jerky movements called saccades. During a saccade, visual input is temporarily suppressed—you do not see while your eyes are moving, but rather during the brief pauses between movements. The brain fills in these gaps, creating the illusion of continuous, stable vision.
🪞Go try this! A fun way to observe this is by looking at your own eyes in a mirror. Try shifting your gaze back and forth between your left and right eye. Even though your eyes are moving, you won’t actually see them move—because visual perception is “offline” during each saccade. Now try it using your cell phone. This time you will see your eyes move because the movement was recorded by the phone’s camera and is delayed.
5 Hearing
The physical energy we experience as sound is actually composed of sound waves—vibrations that travel through air. As an object moves, it displaces the air molecules in front of it. When those molecules bounce back into place, they create alternating zones of high and low pressure that travel outward, much like ripples spreading across a pond after a rock is thrown in. These ripples are the sound waves we hear, which travel much slower than light. A familiar example is the delay between lightning and thunder—light travels at roughly 186,000 miles per second, while sound moves much slower at around 770 miles per hour (about 0.2 miles per second).
Just as the eye has systems for transmission and transduction, so does the ear. The transmission system involves the outer and middle ear, which are responsible for collecting and amplifying sound. The outer ear consists of the pinna (ear lobe) and ear canal, which collect sound and direct it toward the middle ear. The middle ear contains the eardrum and three tiny bones—the malleus, incus, and stapes—which vibrate in response to sound waves. These structures convert air pressure changes into mechanical vibrations.
The transduction system resides in the inner ear, primarily in the cochlea—a coiled, fluid-filled tube. Vibrations from the middle ear cause waves in the cochlear fluid, which in turn stimulate the basilar membrane, where the auditory receptor cells, known as hair cells, are located. These hair cells convert mechanical vibrations into electrical impulses, which are sent to the brain via auditory neurons. Interestingly, the auditory system has significantly fewer neurons than the visual system—around 31,000 auditory neurons compared to over 1 million visual neurons.
The human perceptual experience of sound is based on the physical properties of sound waves. These include frequency, which we perceive as pitch; amplitude, which we experience as loudness; and complexity, which we perceive as timbre (or sound quality).
Humans can typically detect sounds within a frequency range of about 20 Hz to 20,000 Hz (20 kHz). However, our sensitivity to sound changes with age. As we grow older, the outer hair cells in the cochlea—which help amplify sound vibrations—gradually become damaged. This cellular loss makes it particularly difficult to perceive high-frequency sounds, which is why many older adults may not hear ultrasonic tones or high-pitched speech as clearly.
🔎 Explore This (Optional):
Curious about high-frequency sounds that some people can hear but others can’t? Follow this link to a Ultrasonic Ringtones website to test your hearing range and explore ultrasonic tones—frequencies that are often only audible to younger ears.
What is normal in terms of frequency (pitch) and amplitude (loudness)? While humans are capable of hearing frequencies in the range of 20 Hz to 20,000 Hz, we don’t typically experience this full spectrum in everyday life. For example, the human voice usually falls within the 100 to 1,000 Hz range. Musical instruments have a broader range, but even a piano—one of the most wide-ranging acoustic instruments—spans from about 27 Hz (lowest note) to 4,186 Hz (highest note). In daily environments, most of the sounds we encounter tend to cluster within the 100 to 5,000 Hz range, where human hearing is most sensitive.
In terms of loudness, we measure sound using decibels, or dB. The figure below will give you a sense of the range of dB, from barely perceptible sounds to extremely loud and harmful levels.
👂 Clinical Insight:
Protecting your hearing is critical, especially because damage to hair cells is permanent. Prolonged exposure to sounds above 85 decibels (dB) can lead to noise-induced hearing loss. Common culprits include lawn mowers (~90 dB), concerts (~100–110 dB), and headphones at maximum volume (~105 dB). Sounds above 120 dB—such as a siren or jet engine—can cause immediate damage, even with brief exposure. The best way to preserve your hearing is to wear hearing protection in loud environments, limit duration and volume of headphone use, and take quiet breaks during prolonged exposure to noisy settings.
6 Smell
The sense of smell plays a critical role in human survival, helping us detect dangers such as spoiled food, gas leaks, or fire.
However, compared to many animals, humans are far less dependent on smell. In humans, the olfactory cortex occupies about 1/20 of the cerebral hemisphere, while in dogs it takes up nearly 1/3 of the hemisphere—reflecting their vastly superior scent capabilities.
Pheromones, chemical signals related to social and biological behavior, have some influence on humans (e.g., mother-infant bonding, recognizing familiar clothing, or the synchronization of menstrual cycles), but these effects are generally indirect and far less pronounced than in other mammals.
Inside the nasal cavity, cilia (tiny hair-like structures) of olfactory receptor neurons house receptor proteins that bind volatile molecules released into the air. These receptors initiate the transduction process, converting chemical signals into electrical impulses. These signals travel first to the olfactory bulb, and then to areas of the brain involved in emotion and memory—most notably, the amygdala and hippocampus. This unique wiring is why scent is so strongly linked to memory—a specific smell can often trigger vivid emotional recollections.
Scientists estimate that a healthy person can distinguish at least thousands of different odors, with some estimates ranging from 10,000 to over a trillion possible scent combinations, though the precise number remains debated. Experts such as winemakers or perfumers can often identify and discriminate far more scents than the average person due to training and experience.
7 Taste
Although we often give the tongue credit for determining whether something tastes good, taste is actually a multisensory experience, heavily influenced by smell. People who lose their sense of smell (anosmia) often report that food becomes bland or indistinguishable, highlighting the importance of olfactory input in flavor perception.
The tongue—along with parts of the throat, roof of the mouth, and the upper esophagus—contains small bumps called papillae, many of which house taste buds. Taste buds contain taste receptor cells with tiny hair-like projections called microvilli. These microvilli respond to chemical molecules in food and initiate the transduction process, converting chemical signals into neural impulses that are sent to the brain.
There are five basic taste qualities (not four, as was traditionally believed): - Sweet (e.g., sucrose) - Sour (e.g., hydrochloric acid) - Salty (e.g., sodium chloride) - Bitter (e.g., quinine) - Umami (e.g., glutamate, found in savory foods like soy sauce or meat)
While there’s a spatial aspect to how we perceive tastes like sweet, bitter, salty, sour, and umami, its true significance remains unclear. Taste sensitivity does vary slightly across different areas of the mouth, even though the old “tongue map” has been debunked. Small differences in taste detection exist between regions like the tongue, soft palate, and pharynx, and sometimes people misjudge where a taste is located due to interactions with touch sensations. Differences in taste response along the length of the tongue may relate to how the body decides to ingest or expel certain substances. Understanding these spatial patterns might help explain how taste works and why different parts of the mouth respond differently to taste stimuli.
Evidence also shows that taste preference is highly subjective and shaped by cultural, social, and environmental factors. What is delicious in one culture may be unpalatable in another, and exposure to certain flavors over time can shape long-term preferences.
🐟 Fun Fact! Taste preferences vary hugely across cultures—and some delicacies might seem quite strange if you didn’t grow up eating them. For example, in Iceland, some people enjoy hákarl, fermented shark with a strong ammonia smell, while in parts of Southeast Asia, durian fruit is prized by some for its sweet taste despite a famously pungent smell often compared to onions or gym socks. Meanwhile, in Sweden, surströmming (fermented herring) is so odorous it’s often eaten outdoors! These examples show how cultural experiences shape what tastes and smells we learn to love—or avoid.
8 Touch
The sense of touch (also known as somatosensation) allows us to perceive pressure, vibration, temperature, and pain through specialized receptors in the skin. These receptors—such as Meissner’s corpuscles (light touch), Pacinian corpuscles (vibration), Merkel cells (pressure), and free nerve endings (pain and temperature)—convert physical stimuli into electrical impulses through transduction.
These impulses travel through sensory neurons to the spinal cord and then to the somatosensory cortex in the brain, where the information is processed and interpreted. Different parts of the body have varying levels of touch sensitivity, with areas like the fingertips, lips, and face having the highest concentration of receptors.
🎥 Watch This: Follow this link to a YouTube video on the topic of synesthesia, a phenomenon that causes sensory crossovers, such as tasting colors or feeling sounds.
9 Perception
So far, we’ve introduced how the body receives sensory information from the environment. But then what? How does the mind process that information and turn it into something meaningful?
You might hope that humans interpret the world objectively, but as we’ll see, the human experience is actually highly subjective. Our perceptions are shaped not only by the raw sensory input but also by how the brain organizes, filters, and interprets that input.
In the visual system, information is processed through a hierarchical series of brain regions. Visual signals travel from the retina to the primary visual cortex (V1) and then to secondary and higher-order visual areas. Each level refines and integrates information, building up from simple features (like edges or orientation) to more complex and coherent visual experiences. Other senses follow a similar pattern.
Groundbreaking research by Hubel and Wiesel (1968) demonstrated this principle in action. Using electrodes in the visual cortex of anesthetized animals, they identified receptive fields—specific neurons in the primary visual cortex that respond to precise features of visual input, such as a line at a certain angle. Their findings supported the idea that perception emerges from the layered activation of increasingly complex neural networks.
At the highest levels of the visual processing streams, brain regions become highly specialized—so much so that some researchers have theorized the existence of small clusters of cells, or even single neurons, that respond to the identification of specific individuals (e.g., the so-called “grandmother neuron”).
🧠 Did you know?
The idea behind today’s powerful deep learning and neural network AI systems owes a huge debt to the work of cognitive psychologists and neuroscientists working in the mid to late 20th century. Research by scientists like Hubel and Wiesel demonstrated how the brain processes information through layers of neurons that build simple features into more complex patterns. This same principle is used in modern AI systems, where layers of artificial neurons learn to recognize patterns, make predictions, and solve complex tasks—mimicking how your brain processes the world!
9.1 Gestalt Principles
In order to make sense of the visual world, our brains must be able to group elements together into coherent forms. Gestalt psychologists studied this extensively and proposed several foundational principles of perceptual organization—or “rules” the brain tends to follow when interpreting visual input.
These principles include:
- Similarity – We group objects that look alike (e.g., same shape or color).
- Proximity – Objects that are close together are perceived as part of the same group.
- Closure – We tend to fill in gaps to perceive complete, whole objects.
- Good Continuation – We prefer continuous, smooth patterns over abrupt changes or disjointed elements.
- Prägnanz (Simplicity) – We organize visual input into the simplest, most stable, and coherent form possible, even if the input is ambiguous or fragmented.
These rules help the brain organize complex scenes quickly and efficiently, allowing us to recognize patterns and objects with ease—even when information is incomplete or ambiguous.
🎥 Watch This: Follow this link to a Khan Academy video that demonstrates each of the Gestalt principles discussed above.
Another important principle is Figure/Ground. We instinctively separate visual scenes into a focal object (figure) and a background (ground). This distinction is essential for localizing objects in space, allowing us to navigate our environment, avoid obstacles, and interact with the world effectively. Before we can recognize what something is, we must first determine what to focus on—a process that happens automatically in the brain. However, this distinction can sometimes be ambiguous or even reversible, especially in certain artistic or optical illusions.
Painters and designers often exploit the instability of this relationship. For example, in figure–ground illusions, smaller or more enclosed regions are typically perceived as the figure, while larger or surrounding areas are seen as the background. Interestingly, while we may intellectually understand that both interpretations exist, we can usually see only one at a time.
🎥 Watch this before continuing!
9.2 Motion Cues
Motion cues help us perceive movement and depth in our visual environment. When objects move relative to us or the background, our brains use that change in position over time to infer speed, direction, and distance. This is especially useful when navigating through space, detecting threats, or recognizing actions.
A special kind of motion perception is biological motion—the ability to detect movement patterns specific to living beings. Even when shown as just a few moving dots (as in point-light displays), humans can readily perceive complex actions like walking, dancing, or jumping. This suggests that our brains are tuned to recognize the unique motion signatures of animate objects.
🔎 Explore This: Follow this link to a BIO MOTION LAB website to see how your brain can identify human movement—even from just a few animated dots!
9.3 The Power of Expectations
Perception is not just about what enters our eyes or ears—it’s also shaped by what our brains expect to see. This idea is known as perceptual set: the influence of prior experience, context, or expectation on how we interpret sensory input.
To demonstrate this, imagine dividing a class into two groups. Students on the right side of the room are asked to close their eyes while students on the left read the phrase: “Quack Quack!”. Then, the roles reverse—students on the left side close their eyes while those on the right read: “Carrot eater!”
After both groups have heard their respective phrases, everyone views the following image:
What do you think would happen? Typically, students who heard “Quack Quack!” tend to perceive a duck, while those primed with “Carrot eater!” are more likely to see a rabbit. This classic demonstration shows that even when everyone sees the same physical image, our expectations and prior context can shape how we interpret it.